Power supply with uninterruptible function

ABSTRACT

A power supply provided with: an AC/DC converter which receives AC power, converts the AC power into DC power, and outputs the DC power; a DC/DC converter which receives the DC power from the AC/DC converter, and controls a level of an output voltage of the DC/DC converter to be equal to a level of a voltage to be used by a load while the DC/DC converter supplies the output voltage to the load; a DC converter which is connected to an input of the DC/DC converter; and a DC power storage means which supplies electric power to the DC/DC converter through the DC converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/469,619filed on Dec. 22, 1999 now U.S. Pat. No. 6,795,322. The contents ofapplication Ser. No. 09/469,619 are hereby incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a power supply for converting an ACinput into DC power so as to supply the DC power to a load, andparticularly relates to such a power supply having an uninterruptiblefunction.

A communication/information appliance such as a disk array apparatusreceives a commercial AC input, makes an AC/DC converter convert the ACinput into a desired DC voltage required by a load in the appliance, andsupplies the DC voltage to the load. In order to improve reliability ofa power supply in the appliance, AC/DC converters are put in parallelredundant operation. Further, in order to improve reliability on thecommercial AC, the inputs to the AC/DC converters are obtained from twoAC systems. Further, in order to achieve high reliability on thecommercial AC input, a power supply configuration provided with anuninterruptible power supply (hereinafter referred to as UPS) at theoutside is used. A main circuit of the UPS connected is composed of anAC/DC converter, a battery, an inverter, and a change-over switch.Normally, the battery is charged while DC power is supplied to theinverter by the AC/DC converter, so that the DC power is converted intostable AC power by the inverter and the stable AC power is supplied tothe communication/information appliance. When the AC input isinterrupted, the DC power of the battery is converted into AC power bythe inverter so that the AC power is supplied to thecommunication/information appliance. When a failure occurs in the insideof the UPS, power supply is changed to a bypass so that an AC input issupplied to the communication/information appliance directly.Incidentally, as a specific example of the aforementioned backgroundart, there is a power supply described in JP-A-7-194118.

In the background-art power supply configuration, in a normal operationmode, there are two stages of power conversion in the inside of the UPSand a converter for converting AC power into DC power directly in thecommunication/information appliance side. That is, three stages of powerconversion are required. Accordingly, conversion efficiency is worsened.Moreover, because the background-art power supply configuration is madeso that a plurality of stages of converters having overlapping functionsare connected, the volume of the power supply is large and the costthereof is high. Further, with the advance of diversification ofcommunication/information appliances, the power supply is, in mostcases, formed to correspond to a wide-range input so that any appliancecan be selected on the user side without awareness of an input voltage.When an external UPS is connected, there is, however, a problem that theUPS of an input voltage specification adapted to the user environmentmust be selected because the input/output voltage specification of theUPS is fixed.

SUMMARY OF THE INVENTION

The present invention is a result of a trial in consideration of solvingthe aforementioned problems. A power supply according to the presentinvention comprises: an AC/DC converter by which AC power received as aninput is converted into DC power as an output; a DC/DC converter bywhich the level of an output voltage of the DC/DC converter iscontrolled to be equal to the level of a voltage to be used by the loadwhile the DC power received as an input is supplied to a load; a DCconverter connected to the input of the DC/DC converter; and a DC powerstorage means for supplying electric power to the DC/DC converterthrough the DC converter.

According to the present invention, a high-reliable DC power supplyhaving an uninterruptible function can be achieved.

Preferably, the DC converter is configured so that the output voltage ofthe DC converter is controlled to be boosted over the voltage of the DCpower storage means while electric power supplied from the DC powerstorage means is supplied to the input of the DC/DC converter. Such apreferable configuration of the DC converter is provided with: a firstconverter having an AC terminal, and a DC terminal connected to theinput of the DC/DC converter; a transformer having a high-voltage sidewinding connected to the AC terminal of the first converter, and alow-voltage side winding; and a second converter having an AC terminalconnected to the low-voltage side winding of the transformer, and a DCterminal connected to the DC power storage means. According to thisconfiguration, both charge and discharge of the DC power storage meanscan be performed even in the case where the level of the voltage of theDC power storage means is different from the level of the output voltageof the AC/DC converter, that is, the level of the input voltage of theDC/DC converter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of the present invention;

FIG. 2 shows a second embodiment of the present invention;

FIG. 3 shows a detailed configuration of the second embodiment of thepresent invention;

FIG. 4 shows a third embodiment of the present invention;

FIG. 5 shows a fourth embodiment of the present invention;

FIG. 6 shows a fifth embodiment of the present invention;

FIG. 7 shows a sixth embodiment of the present invention;

FIG. 8 shows a seventh embodiment of the present invention;

FIG. 9 shows an example of a bridge type converter; and

FIG. 10 shows an example of a 1-transistor forward converter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a power supply according to a first embodiment of thepresent invention. The power supply is provided with an AC/DC converter1 for converting supplied AC power into DC power; a battery 4; a DCconverter 3 for converting DC power of the battery 4 into a DC voltageof a level substantially equal to the level of the DC output voltage ofthe AC/DC converter 1; and a DC/DC converter 2 for converting the DCoutput power of the AC/DC converter 1 or of the DC converter 3 into a DCvoltage required by a load 5. A diode bridge rectifier circuit, or abridge converter and phase rectifier circuit having a semiconductorswitching device as shown in FIG. 9, or the like, can be used as theAC/DC converter 1. A 1-transistor forward converter shown in FIG. 10, orthe like, can be used as the DC/DC converter 2. When the configurationis made so that DC power is supplied to the DC/DC converter 2 from theAC/DC converter 1 and the DC converter 3, stable power can be suppliedto the load 5 from the DC/DC converter 2 even in case of an accident ofthe AC input. Incidentally, a main circuit of the DC converter 3 isconstituted by a converter 32 a, a transformer 32 c, and a converter 32b in order to boost the relatively low DC voltage (for example, about 40V to about 50 V) of the battery 4 to the level (for example, about 300 Vto about 400 V) of the DC output voltage of the AC/DC converter 1 whichis higher than the level of the DC voltage of the battery 4, or in orderto improve the separation and utilization factor of earth potential.That is, the DC converter 3 is configured so that the battery 4 isconnected to a DC terminal of the converter 32 b whereas a low-voltageside winding of the transformer 32 c is connected to an AC terminal ofthe converter 32 b. Further, a high-voltage side winding of thetransformer 32 c is connected to an AC terminal of the converter 32 awhereas a DC terminal of the converter 32 a is connected both to the DCoutput of the AC/DC converter 1 and to the DC input of the DC/DCconverter 2. A bridge converter as shown in FIG. 9, or the like, can beused as each of the converters 32 a and 32 b.

In a normal mode, the AC/DC converter 1 is supplied with commercial ACpower of 100 V or 200 V as an input and converts the input AC power intoDC power as an output. The DC output voltage from the AC/DC converter 1is higher (for example, 300 V to 400 V) than the effective value of theAC input voltage. The DC output power from the AC/DC converter 1 issupplied as an input to the DC/DC converter 2. The DC/DC converter 2controls the level of its DC output voltage to be equal to the level ofa voltage to be required by the load 5 while the DC/DC converter 2supplies the given DC power to the load 5. The DC output power of theAC/DC converter 1 is supplied to the DC terminal of the converter 32 a.The converter 32 a operates as a DC/AC converter, that is, as aninverter, so as to convert the input DC power into AC power on the basisof the ON/OFF operation of a semiconductor switching device to therebysupply the AC power to the high-voltage side winding of the transformer32 c. The transformer 32 c drops the AC input voltage applied to itshigh-voltage side winding and outputs the dropped AC voltage at itslow-voltage side winding. The AC output power at the low-voltage sidewinding is supplied to the AC terminal of the converter 32 b. Theconverter 32 b operates as an AC/DC converter so as to convert the inputAC power into DC power on the basis of the ON/OFF operation of a dioderectifier and semiconductor switching device to thereby supply the DCpower from its DC terminal of the converter 32 b. The DC output powerfrom the converter 32 b is stored in the battery 4 so that the battery 4is charged. That is, the DC converter 3 is supplied with the DC power ofthe AC/DC converter 1 as its input and controls its output voltage to belower than the output side voltage of the AC/DC converter 1 while itoutputs the DC power as its output. Thus, the battery 4 is charged withthe DC output power of the DC converter 3 so that DC power is stored inthe battery 4.

On the contrary, in case where the AC/DC converter 1 cannot supply powerat all or enough to be consumed by the load because of powerinterruption, or the like, the battery 4 supplies DC power to the DCterminal of the converter 32 b. The converter 32 b operates as a DC/ACconverter, that is, as an inverter, so as to convert the DC input powerinto AC power on the basis of the ON/OFF operation of the semiconductorswitching device and supplies the AC power to the low-voltage sidewinding of the transformer 32 c. The transformer 32 c the AC power atits high-voltage side winding with boosting the AC voltage supplied toits low-voltage side winding. The AC output power at the high-voltageside winding is supplied to the AC terminal of the converter 32 a. Theconverter 32 a operates as an AC/DC converter so as to convert the ACinput power into DC power on the basis of the ON/OFF operation of thediode rectifier and semiconductor switching device and outputs the DCpower from its DC terminal. The DC/DC converter 2 is supplied with theDC output power of the converter 32 a as its input and controls thelevel of its DC output voltage to be equal to the level of the voltageto be used by the load 5 while it supplies the supplied DC power to theload 5. That is, the DC converter 3 makes a control to boost its DCoutput voltage to be over the DC voltage of the battery 4 while itsupplies DC power discharged from the battery 4 to the input of theDC/DC converter 2.

As described above, an uninterruptible DC power supply system in whichthe DC input voltage of the DC/DC converter 2 is backed up by the DCconverter 3 can be provided according to the embodiment of FIG. 1.Hence, reliability can be improved. Moreover, the system can beprevented from having power conversion portions with overlappingfunctions. Hence, reduction in size and cost and improvement inconversion efficiency can be achieved. Moreover, the DC converter 3 isprovided with the converters 32 a and 32 b having semiconductorswitching devices respectively, and the transformer 32 c. Hence, even inthe case where the level of the voltage of the battery 4 is greatlydifferent from the level of the output voltage of the AC/DC converter 1,that is, from the level of the input voltage of the DC/DC converter 2,both charge and discharge of the battery 4 can be carried out, andvoltage, level conversion can be made between the voltage level of thebattery 4 and the output voltage level of the AC/DC converter 1 with lowpower loss. Hence, according to the embodiment, a power supply of highreliability and low loss can be achieved. Incidentally, the battery 4 inthis embodiment may be replaced by any other DC power storage means suchas a secondary battery, a capacitor, an electric double layer, or thelike.

FIG. 2 shows a power supply according to a second embodiment of thepresent invention. The point of difference of this embodiment from theembodiment of FIG. 1 is that the power supply according to thisembodiment is further provided with a charger 6 connected to an AC inputso as to convert AC power supplied from the AC input into DC power sothat the battery 4 is charged with the DC power obtained from the ACinput by the charger 6. With this configuration, the function ofcharging the battery 4 through the DC converter 3 is not required.Hence, the DC converter 3 does not operate in a normal mode but operatesin a power interruption mode in the same manner as in the embodiment ofFIG. 1. According to the embodiment of FIG. 2, the DC converter 3 can beprovided to have a single function of unidirectional power conversion.Hence, reliability can be improved more greatly, and reduction in sizeand cost and improvement in conversion efficiency can be achieved.Incidentally, a circuit shown in FIG. 9, a diode bridge rectifier, orthe like, can be used as the charger 6. Moreover, because the batterycharging function of the DC converter 3 is not required, the converter32 a may be constituted by a simple diode rectifier so that the circuitconfiguration of the converter 32 a is simplified.

FIG. 3 shows a more detailed configuration of the embodiment of FIG. 2.The AC/DC converter 1 is constituted by a control circuit 11, a powerinterruption detection signal circuit 11 a, and a main circuit 12 havinga power-factor improvement function. The AC/DC converter 1 receives acommercial AC input and outputs DC power. It is a matter of course thatthe control circuit 11 controls the output voltage of the AC/DCconverter 1 to be equal to a predetermined DC voltage on the basis ofthe ON/OFF actuation of a semiconductor switching device of the maincircuit 12 such as a circuit of FIG. 9 according to an ON/OFF signalwhich serves as an actuating command. Further, the control circuit 11has a power-factor improvement function and hence performs controllingto suppress harmonic current in the AC input. The power interruptiondetection signal circuit 11 a has a function of monitoring the AC inputand detecting an accident, or the like. When power interruption isdetected, the power interruption detection signal circuit 11 a generatesa power interruption detection signal and applies the signal to the DCconverter 3. That is, the power interruption detection circuit 11 acompares the voltage level of the AC input with a reference voltagelevel and sends a power interruption detection signal to the DCconverter 3 when the voltage level of the AC input is lower than thereference voltage level. The DC/DC converter 2 includes a controlcircuit 21, and a main circuit 22. The control circuit 21 drives asemiconductor switching device of the main circuit 22 (for example, acircuit of FIG. 10) to switch ON/OFF according to an ON/OFF signal whichserves as an actuating command. The main circuit 22 is supplied with DCpower from the AC/DC converter 1 or from the DC converter 3, convertsthe supplied DC power into DC power required by the load 5, and thensupplies the converted DC power to the load 5. The DC converter 3 isconstituted by a control circuit 31, a main circuit 32, and an actuatingsignal generating circuit 33. The actuating signal generating circuit 33is supplied with a power interruption detection signal and an actuatingcommand. When a power interruption detection signal is received from thepower interruption detection circuit 11 a, the actuating signalgenerating circuit 33 sends an input actuating command to the controlcircuit 31. In a normal mode in which no power interruption detectionsignal is supplied, the actuating signal generating circuit 33 does notsend out the actuating command. In this embodiment, an AND circuit isused in the actuating signal generating circuit 33. In a powerinterruption mode, the level of the power interruption detection signalinput to the AND circuit is high (1). In this mode, when the actuatingcommand is ON (that is, the level of the actuating command is high (1)),the level of the output of the AND circuit is high (1), that is, theoutput of the AND circuit is ON. In this mode, on the other hand, whenthe actuating command is OFF (that is, the level of the actuatingcommand is low (0)), the level of the output of the AND circuit is low(0), that is, the output of the AND circuit is OFF. That is, the outputof the actuating signal generating circuit 33 is an ON/OFF signalsimilar to the ON/OFF signal as the actuating command. On the otherhand, in a normal mode, the level of the power interruption detectionsignal is low (0). In this mode, therefore, the level of the output ofthe AND circuit is low (0) irrespective of the ON/OFF signal as theactuating command. Hence, no signal corresponding to the actuatingcommand signal is produced from the AND circuit. When a powerinterruption detection signal is applied in case where the AC input isinterrupted, the control circuit 31 is supplied with the ON/OFF signalfrom the actuating signal generating circuit 33 and drives thesemiconductor switching device of the main circuit 32 to switch ON/OFF.Hence, the main circuit 32 operates to convert the DC power of thebattery 4 into a DC voltage substantially equal to the output voltage ofthe AC/DC converter 1 and supply the DC voltage to the DC/DC converter2. The charger 6 is constituted by a control circuit 61, and a maincircuit 62. The control circuit 61 is supplied with the ON/OFF signal asthe actuating command and drives a semiconductor switching device of themain circuit 62 to switch ON/OFF. Hence, the main circuit 62 convertsthe AC input into DC power so as to charge the battery 4 with a voltageor current in accordance with the battery charging state. According tothe power supply of FIG. 3, an uninterruptible DC power supply system inwhich the DC input voltage of the DC/DC converter 2 is backed up by theDC converter 3 can be provided. Hence, reliability can be improved.Moreover, the system does not have any power conversion portions havingoverlapping functions. Hence, it is possible to achieve a power supplyin which reduction in size and cost and improvement in conversionefficiency can be attained.

FIG. 4 shows a power supply according to a third embodiment of thepresent invention. In FIG. 4, circuit constituent parts such asconverters, or the like, designated by the same reference numerals usedin FIG. 3 designate the same circuit constituent parts as described inthe embodiment shown in FIGS. 2 and 3. In the embodiment of FIG. 4, theAC/DC converter 1 is constituted by a plurality of unit AC/DC convertersconnected in parallel with one another, the DC/DC converter 2 isconstituted by a plurality of unit DC/DC converters connected inparallel with one another and the DC converter 3 is constituted by aplurality of unit DC converters connected in parallel with one another.Each of the unit AC/DC converters, the unit DC/DC converters and theunit DC converters is constituted by a module unit or a semiconductorintegrated circuit which is built in one casing or mounted on onecircuit board. The number of the unit AC/DC converters connected inparallel with one another, the number of the unit DC/DC convertersconnected in parallel with one another and the number of the unit DCconverters connected in parallel with one another are selected inaccordance with the load capacity and the purpose of use. The circuitoperations thereof are the same as in the embodiment of FIG. 3. Further,each of circuit constituent parts of the unit DC converters isconstituted by a module unit and the number of the unit DC convertersconnected in parallel with one another is selected in accordance withthe load capacity and the purpose of use. In the configuration in whichcircuit constituent parts are arranged in parallel with one other so asto be multiplexed as shown in FIG. 4, electric power can be supplied tothe load 5 securely even in case where any unit circuit constituent partbreaks down. Moreover, for maintenance and exchange of the unit circuitconstituent parts, any unit circuit constituent part can be exchanged toa new one without stopping the power supply. According to the embodimentof FIG. 4, an interruptible DC power supply in which the DC inputvoltage of the DC/DC converter 2 is backed up by the DC converter 3 canbe provided. Moreover, reliability is improved more greatly because thecircuit constituent parts are multiplexed. Moreover, a power supply ofeasily variable power capacity can be achieved because the number of thecircuit constituent parts connected in parallel with one another can beselected in accordance with the required capacity and the purpose ofuse.

FIG. 5 shows a power supply according to a fourth embodiment of thepresent invention. This embodiment shows a power supply configuration inwhich a plurality of power supply units each formed in such a manner asdescribed in the embodiment shown in FIGS. 2 and 3 are arranged inparallel with one another so as to be multiplexed. Incidentally, theDC/DC converters 2 have a function of permitting parallel operation. Inthe multiplex configuration as shown in FIG. 5, electric power can besupplied to the load 5 securely even in case where any one of the powersupply units breaks down. Moreover, for maintenance and exchange of thepower supply units, any power supply unit can be exchanged to a new onewithout stopping the power supply. Moreover, because each power supplyunit has a charger and a battery, power supply to the load can becontinued even in case where a part of the chargers or a part of thebatteries breaks down. Hence, reliability against a failure in chargersand batteries is improved. Moreover, a charger 6 and a battery 4 may beused in common to all the power supply units so that DC power from onebattery can be supplied in common to the respective DC converters 3 ofthe power supply units.

FIG. 6 shows a power supply according to a fifth embodiment of thepresent invention. In FIG. 6, circuit constituent parts such asconverters, or the like, designated by the same reference numerals asshown in FIG. 3 designate the same circuit constituent parts asdescribed in the embodiment shown in FIGS. 2 and 3. The point ofdifference of the embodiment shown in FIG. 6 from the embodiment shownin FIGS. 2 and 3 is that a DC input of a DC/DC converter 7 is connectedto the DC output of the AC/DC converter 1 and a DC input of a DC/DCconverter 8 is connected to a DC output of the DC/DC converter 7. TheDC/DC converter 8 is constituted by a plurality of unit DC/DC convertersconnected in parallel with one another so as to be multiplexed. The unitDC/DC converters have a common DC input, and a common DC output. Thecommon output of the unit DC/DC converters is connected to the load. Thecommon input of the unit DC/DC converters is connected to the output ofthe DC/DC converter 7. Further, the DC terminal of the DC converter 3 isconnected both to the DC output of the DC/DC converter 7 and to thecommon DC input of the DC/DC converter 8.

In FIG. 6, the AC/DC converter 1 is supplied with AC power from the ACinput and controls the output voltage level of the AC/DC converter 1 tobe a first DC voltage level while it converts the AC power into DCpower. The DC power is supplied to the DC/DC converter 7. The DC/DCconverter 7 controls the DC output voltage level of the DC/DC converter7 to be a second DC voltage level which is lower than the first DCvoltage level while it outputs and supplies the input first DC power tothe DC/DC converter 8. The DC converter 3 controls the output voltagelevel of the DC converter 3 to be substantially equal to the second DCvoltage level while it outputs and supplies DC power stored in thebattery to the output side of the DC/DC converter 7. The DC/DC converter8 controls the DC output voltage level of the DC/DC converter 8 to be aDC voltage level to be used by the load 5 while it outputs and suppliesDC power given from the DC/DC converter 7 or from the DC converter 3 tothe load 5. Incidentally, it is a matter of course that each of theAC/DC converter 1, the DC/DC converter 7, the DC converter 3 and theportion of combination of the charger 6 and the battery 4 may beprovided as a multiplex structure as shown in FIG. 4 or 5. Further,power supply configuration may be made so that the portion ofcombination of the charger 6 and the battery 4 is provided outside thepower supply. In the embodiment of FIG. 6, the input voltage level ofthe DC/DC converter 8 can be made lower than the first DC voltage level,so that maintenance and exchange of the multiplex DC/DC converter 8 canbe made more safely.

FIG. 7 shows a power supply according to a sixth embodiment of thepresent invention. In FIG. 7, circuit constituent parts such asconverters, or the like, designated by the same reference numerals asused in FIG. 6 are the same as shown in FIG. 6. FIG. 7 shows the casewhere the plurality of unit DC/DC converters constituting the DC/DCconverter 8 shown in FIG. 6 are divided into a plurality of groups (unitDC/DC converter groups) 8 a and 8 b. Each of the DC/DC converter groups8 a and 8 b has a DC input and a DC output which are common to theplurality of unit DC/DC converters belonging to the group. Therespective common DC inputs of the unit DC/DC converter groups 8 a and 8b are connected to the DC output of the DC/DC converter 7. The common DCoutputs of the unit DC/DC converter groups 8 a and 8 b are connected toloads 5 a and 5 b, respectively. The loads 5 a and 5 b are independentload portions constituting the load 5. In each of the unit DC/DCconverter groups 8 a and 8 b in the embodiment of FIG. 7, a plurality ofunit DC/DC converters are arranged in parallel with one another so as tobe multiplexed. Hence, even in case where any one of the unit DC/DCconverters breaks down with respect to any one of the loads 5 a and 5 b,power supply to the load can be continued by the other unit DC/DCconverter. Accordingly, a power supply of high reliability for supplyingelectric power to a plurality of loads can be achieved.

FIG. 8 shows a power supply according to a seventh embodiment of thepresent invention. In FIG. 8, circuit constituent parts such asconverters, or the like, designated by the same reference numerals asshown in FIG. 6 are the same as shown in FIG. 6. In the embodiment ofFIG. 8, a plurality of unit DC/DC converters 8 a, 8 b, 8 c and 8 d areprovided as the DC/DC converter 8 shown in FIG. 6. Respective DC inputsof the unit DC/DC converters 8 a, 8 b, 8 c and 8 d are connected to theDC output of the DC/DC converter 7. DC outputs of the unit DC/DCconverters 8 a, 8 b, 8 c and 8 d are connected to independent loadportions 5 a, 5 b, 5 c and 5 d respectively. The independent loadportions constitute the load 5. In this embodiment, respective outputvoltage and power levels of the unit DC/DC converters 8 a–8 d can beadjusted independently in accordance with the load portions.Accordingly, a power supply of high reliability permitting electricpower to be supplied to a plurality of loads different in powerconsumption and in applied voltage level can be achieved.

Incidentally, the description of each of the second, third, fourth,fifth, sixth and seventh embodiments shows the case where the DCconverter 3 has a single function of unidirectional power conversionfrom the battery side to the DC/DC converter side. As the DC converter3, however, a converter permitting two-way power transmission may beused so that battery charging can be performed by the combination of theDC converter and the charger. Particularly, in the embodiment of FIG. 6,there may be provided a power supply which uses a DC converterpermitting two-way power transmission as the DC converter so that thebattery 4 is charged with DC power obtained from the front DC/DCconverter 7 when the AC input is normal whereas a DC voltage from thebattery 4 is supplied to the post-stage DC/DC converter 8 when the ACinput is interrupted. In addition, the number of parallel arrangementsof each circuit constituent part and the number of load portions are notlimited to the numbers shown in the drawings and may be determined atoption.

According to the present invention, a power supply of high reliabilityfor supplying DC power to a load can be achieved.

1. A power supply comprising: an AC/DC converter which converts an inputAC power into DC power and outputs the DC power to an output terminalthereof, said AC/DC converter having power factor improvement function;a DC/DC converter having an input terminal connected to the outputterminal of said AC/DC converter, said DC/DC converter converting a DCvoltage inputted thereto into a voltage value to be applied to a load; aDC converter having a first terminal connected to the output terminal ofsaid AC/DC converter and the input terminal of said DC/DC converter; andDC power storage means which is connected to a second terminal of saidDC converters, and which supplies said DC/DC converter with a DC powerthrough said DC converter; wherein said load is supplied with the DCpower from said AC/DC converter through said DC/DC converter, and saidDC power storage means connected to said second terminal of said DCconverter is supplied with the DC power from said AC/DC converter forcharging using a path through the output terminal of said AC/DCconverter, the first terminal of said DC converter and said DCconverter; and wherein, said DC converter comprising an actuating signalgenerating portion having an AND logic circuit, and said AND logiccircuit is supplied with a power interruption detecting signal and anactuating command, and when the input AC power is not applied to saidAC/DC converter and said actuating command is ON, said load is suppliedwith the DC power from said DC power storage means using a path throughsaid second terminal, said DC converter, said first terminal and saidDC/DC converter in order.
 2. A power supply according to claim 1,wherein said DC converter comprises: a first converter having an ACterminal, and a DC terminal which is said first terminal connected tothe input terminal of said DC/DC converter; a transformer having ahigh-voltage side winding connected to the AC terminal of said firstconverter, and a low-voltage side winding; and a second converter havingan AC terminal connected to the low-voltage side winding, and a DCterminal which is said second terminal connected to said DC powerstorage means.
 3. A power supply according to claim 1, wherein said DCpower storage means is a secondary battery or a capacitor.
 4. A powersupply according to claim 1, wherein said AC/DC converter is suppliedwith commercial AC power of 100 V to 200 V.
 5. A power supply accordingto claim 1, wherein said DC power storage means voltage is 40 V to 50 V.6. A power supply comprising: an AC/DC converter which converts an inputAC power into DC power and outputs the DC power to an output terminalthereof; a DC/DC converter having an input terminal connected to theoutput terminal of said AC/DC converter, said DC/DC converter convertinga DC voltage inputted thereto into a voltage to be applied to a load; aDC converter having a first terminal connected to the output terminal ofsaid AC/DC converter and the input terminal of said DC/DC converter; anda DC power storage unit which is connected to a second terminal of saidDC converter to receive storage power, and which supplies said DC/DCconverter with a DC power through said DC converter; wherein said loadis supplied with the DC power from said AC/DC converter through saidDC/DC converter, and said DC power storage unit connected to said secondterminal of said DC converter is supplied with the DC power from saidAC/DC converter for charging using a path through the output terminal ofsaid AC/DC converter, the first terminal of said DC converter and saidDC converter; and wherein, said DC converter comprising a back-up poweractuating unit including an AND logic circuit, and where differinginputs of the AND logic circuit are supplied with a power interruptiondetecting signal and a back-up power actuating command signal, and whenboth the power interruption detecting signal indicates that input ACpower is not applied to said AC/DC converter and the actuating commandsignal enables back-up power, said load is supplied with the DC powerfrom said DC power storage unit using a path through said secondterminal, said DC converter, said first terminal and said DC/DCconverter.
 7. A power supply according to claim 6, wherein said DCconverter comprises: a first converter having an AC terminal, and a DCterminal which is said first terminal connected to the input terminal ofsaid DC/DC converter; a transformer having a high-voltage side windingconnected to the AC terminal of said first converter, and a low-voltageside winding; and a second converter having an AC terminal connected tothe low-voltage side winding, and a DC terminal which is said secondterminal connected to said DC power storage unit.
 8. A power supplyaccording to claim 6, wherein said DC power storage unit is a secondarybattery or a capacitor.
 9. A power supply according to claim 6, whereinsaid AC/DC converter is supplied with commercial AC power of 100 V to200 V.
 10. A power supply according to claim 6, wherein said DC powerstorage unit voltage is 40 V to 50 V.